The efficacy of hot water dipping and UV irradiation against apple storage rots caused by Alternaria alternata (mouldy core), Trichothecium roseum (pink mould rot), Monilinia fructigena (brown rot), Aspergillus niger (black rot) and Penicillium expansum (blue mould rot) was examined. Artificially inoculated Starking Delicious apples were incubated for 3 min in a water bath heated to specific temperatures in the range of 48 ˚C to 52 ˚C. Storage rots caused by all the five species were significantly reduced at dipping temperature of 48 ˚C. UV irradiation of fruits for 15 min was found most effective in reducing decays caused by all the test fungi. These results suggest possible applications of hot water dipping and UV irradiation of apples at harvest, after short-term cold storage or after the opening of controlled-atmosphere storage rooms in order to reduce decays during subsequent storage periods. 2.2. Fruit inoculation Fruits were inoculated following Well method of Granger and Horne (1924). Wells were made on the fruit surface with the help of cork borer (internal diameter 5 mm). The inoculum of A. alternata, T. roseum, M. fructigena, A. niger and P. expansum was placed at the bottom of wells and plugged back. These were further sealed with sterile paraffin wax.
Mouldy core and core rot of apple caused by Alternaria alternata has emerged an economically important disease in Himachal Pradesh, India causing direct losses to the growers. The fungus remains dormant inside the calyx of the fruit and later becomes active when the starch content of the fruits get converted into sugar and hence causes the post harvest disease, where the rotting of the fruits starts from the core region. In vitro studies on the effect of temperature and relative humidity on the growth of the conidia of Alternaria alternata causing mouldy core and core rot of apple revealed that, the temperature of 30°C and 100 per cent relative humidity were optimal for conidial germination. Among different weather parameters, cumulative rainfall was directly correlated with disease development. Regression analysis further showed that 91.00 per cent variation in pre-harvest fruit drop was due to mouldy core and core rot. Medium sized Starking Delicious apple fruits with open sinus/calyx tube and length: width ratio falling in 0.96 to 1.05 mm showed maximum incidence of mouldy core and core rot in the field.
Effect of pre-cooling, hot water treatment, fumigation, an antagonist (Bacillus subtilis) along with treatment of apple fruits with extract of Emblica officinalis (amla) and coating with neem oil was evaluated for their activity against the fungal growth of Alternaria alternata and Trichothecium roseum, the causal agents of mouldy core and pink mould rot, respectively. Impregnation of fruit trays with botanical formulations was also integrated with other treatments before placing the treated and untreated fruits in controlled atmosphere (CA) storage for four months. The integration of hydro cooling with ice water+CaCl2 (HIWC)+fruit skin coating with neem oil (1%)+placing treated fruits on botanical formulation (BF) impregnated fruit trays (treatment combination T7) prior to CA storage gave highest inhibition of the pathogenic tested fungi with rot incidence of 16.05, 20.46% and fruit rot of 9.05, 11.46%, respectively. The treatment combination T6 in which the antagonist B. subtilis was integrated with pre-cooling and BF-impregnated trays was the next effective treatment with rot incidence of 20.35, 23.07% and fruit rot of 13.34, 17.08%, respectively.
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